The field of invention relates to semiconductor lithography in general and mask manufacturing techniques that allow for DUV based inspection of EUV reflective masks more specifically.
Masks are used in semiconductor processing to properly form regions of light that are subsequently directed onto a semiconductor substrate. Depending on the type of resist (e.g., positive or negative) that is coated upon the substrate, the regions of light formed by the mask correspond to either the specific structures formed on the surface of the semiconductor substrate (e.g., gate electrodes, source/drain electrodes, vias and interconnect lines, among others) or the spaces between these structures.
Masks are patterned in a manner that corresponds to the structures formed on the substrate. A mask essentially affects the optical path between an exposure light source and the semiconductor substrate. The patterns on the mask prevent various portions of the exposure light from reaching the semiconductor substrate. As such, the mask is patterned with opaque as well as non-opaque regions.
The opaque regions prevent exposure light from reaching the semiconductor substrate. The non-opaque regions allow exposure light to reach the semiconductor substrate. The specific patterning of the mask""s non-opaque regions corresponds to the shape of those regions of light that are subsequently directed onto the semiconductor substrate. Typically, each layer in a semiconductor device has its own corresponding mask that is used to form the specific structures at each layer according to the semiconductor device""s particular design.
Traditionally, transmission masks have been used for Deep Ultra Violet (DUV) lithography associated with semiconductor processing. Transmission masks are essentially inserted into the optical path between the exposure light source and the semiconductor substrate. A transmission mask 100 is shown in FIG. 1a. With transmission masks, the opaque regions 101 absorb and/or reflect exposure light while the non-opaque regions 102 are transparent to the exposure light. The light 103 passing through the non-opaque regions 102 is then directed to the semiconductor substrate surface.
As smaller and smaller device sizes are continually being formed within the semiconductor industry, the wavelength of the exposure light source continues to be reduced. As Extreme Ultra Violet (EUV) technology emerges, reflection rather than transmission masks are being developed. Reflection masks are positioned along the optical path between the exposure light source and the semiconductor substrate. A reflection mask 104 is shown in FIG. 1b. With reflection masks, the opaque regions 105 absorb exposure light while the non-opaque regions 106 reflect exposure light. Thus, for reflective masks, non-opaque regions correspond to reflective regions and opaque regions correspond to non-reflective regions. The light Ireflective reflecting off of the reflective regions 106 is then directed to the semiconductor surface.
During the mask manufacturing process, defects in the mask patterning are searched for, found and corrected. Defects may be searched for at multiple instances during the mask manufacturing process. For example, before and after a buffer layer 107 (of FIG. 1b) is etched. A problem with the manufacturing of masks for EUV applications is that the tools used for the searching of patterning defects may not operate within the EUV spectrum (which, for purposes of this application, corresponds to light at wavelengths within 10-100 nm) but rather, the DUV spectrum (which, for purposes of this application, corresponds to light at wavelengths within 100-300 nm).
Since the mask is designed to affect EUV light, the optical properties of the non-reflective and reflective regions in the EUV spectra may be dissimilar from their optical properties in the DUV spectra. This may result in difficulties when searching for defects. Principally, if the mask does not exhibit a suitable difference between the reflected intensity of inspection tool light at the reflective regions and the non-reflective regions, the defect search tool will have difficulty recognizing the mask patterning and any defects therein.
An apparatus comprising a reflective mask having non-reflective and reflective regions, where the reflective regions are reflective of a first light that has an inspection wavelength and are reflective of a second light that has a semiconductor processing exposure wavelength. The non-reflective regions are less reflective of the first light and the second light than the reflective regions in order to create: 1) a first image with a first contrast that is sufficient to identify defects in the reflective mask and that is formed by reflecting the first light off of the reflective mask; and 2) a second image with a second contrast that is sufficient to expose photoresist that is coated onto a semiconductor substrate and that is formed by reflecting the second light off of the reflective mask.